Stabilization of polymers by incorporation of ultraviolet light stabilizers in polymer films, coatings, fibers, and molded articles to provide protection against the degrading action of light, moisture, or oxygen has been an active area of work in recent years. However, deficiencies such as volatility and generally poor retention of existing stabilizers within a polymer matrix still remain largely unsolved. For example, attempts to reduce volatility by using higher molecular weight oligomers and polymers have generally resulted in a decreased retention of the stabilizer due to incompatibility. Extractibility and migration of the stabilizer to the surface and eventually loss as a result of incompatibility or low molecular weight are still serious problems plaguing the plastics industry.
Limited attempts to increase the molecular weight of the stabilizer without introducing incompatibility by using anchor groups have been made in the past without great success. Among the anchor groups used for supporting stabilizers, triazines have received some attention. U.S. Pat. No. 4,319,016 describes an ultraviolet absorbing material which is the reaction product of (a) a hydroxyphenyl ultraviolet light absorbing compound, (b) formaldehyde, and (c) an amino-group containing compound, such as melamine. It is stated therein that if the hydroxyphenyl compound is present in amounts greater than 0.5 mole per mole of melamine, the amount of unreacted hydroxyphenyl compound frequently increases and the compatibility of the resulting compound with a resin or solvent tends to be reduced. The reaction product obtained by the method described therein is not described in the patent.
U.S. Pat. Nos. 3,535,318; 3,595,602; 4,418,000; 4,418,001; and 4,418,002; and Japense Patent No. 01-287160 describe reaction products obtained by reacting hydroxy group-containing ultraviolet absorbers with alkoxymethyl-group containing aminoplasts. The attachment of the ultraviolet absorbing group of the aminoplast anchor, however, is always through a weak carbon-oxygen bond between the bridging methylene group of the aminoplast and the hydroxy group of the ultraviolet light absorbing component.
U.S. Pat. Nos. 3,316,208; 4,197,392; and 4,913,974; and Canadian Patent No. 1,065,991 describe acid curable compositions containing ultraviolet light absorbers and alkoxymethyl group-containing aminoplast. Despite the presence of acids, there is no suggestion in these references of any reaction between the absorber component and the aminoplast component of said curable compositions.
U.S. Pat. Nos. 4,612,358; 4,652,656; and 3,399,173; Japense Patent No. 63-205334; and a review article in "Caoutchoucs et Plastiques", No. 575, November 1977 describe ultraviolet light absorbing polymerizable monomers and polymers thereof. An article in "Polymer Degradation and Stability," Vol. 25, pages 121-141 (1989) entitled "New Developments in Polymer Stabilization" describes the effects of molecular weight of stabilizers on performance. U.S. Pat. No. 4,355,071 describes clear coat/color coat finishes in which stabilizers are able to migrate across the interface. An article in Journal of Polymer Science, Polymer Letters, Volume 15, Number 11, pages 675 to 677 (1977) and U.S. Pat. Nos. 4,612,358 and 4,652,656 disclose the use of 95 to 98% sulfuric acid in the preparation of polymerizable, benzophenone and benzotriazole type stabilizers. U.S. Pat. No. 4,233,430 similarly discloses the use of sulfuric acid in the preparation of related polymers.
The object of this invention is to provide novel aminoplast-anchored blocked and unblocked phenolic stabilizers.
Another object of this invention is to provide a process for the preparation of the novel stabilizers of the invention.
It is yet another object of this invention to provide curable compositions containing the novel stabilizers of the invention and also provide stabilized cured compositions obtained by curing said curable compositions.
It is yet another object of this invention to provide an improved method of stabilizing polymers wherein the improvement comprises adding to said polymers the novel stabilizers of the invention.